Unity Files Won't Keep Saved Changes

So here I am, getting very annoyed with Unity. I’m on Windows 7 x64, and I’m using the free Unity version, the most recent. This has happened twice in the last week. I’ll edit the scene, edit some prefabs, edit some scripts, save SCENE and PROJECT, save any scripts open, and exit Unity. Sometimes when I get back on, suddenly the edits I made no longer exist and the project files are at the state they were 2-4 days ago, despite the fact that I made absolutely sure to save and re-save scripts while in the editor, the scenes, and the project. I’m really not sure what’s going on, but it’s making it difficult to move forward.

I can’t imagine this happening in a big project; mine’s still small. But I can’t continue using an editor that doesn’t save properly.

Are there points in the saving process I’m missing?

EDIT: To be clear, it doesn’t happen every time, nor does it happen to every file, but it’s done it twice this week.

That sounds very odd. Perhaps there’s something faulty with your windows permissions.
Try changing your Unity shortcut to ‘Run as Administrator’.

Other than that, I’d re-install but that sounds more like a Windows issue than a Unity issue.